%%
%% %CopyrightBegin%
%%
%% Copyright Ericsson AB 2016-2018. All Rights Reserved.
%%
%% Licensed under the Apache License, Version 2.0 (the "License");
%% you may not use this file except in compliance with the License.
%% You may obtain a copy of the License at
%%
%% http://www.apache.org/licenses/LICENSE-2.0
%%
%% Unless required by applicable law or agreed to in writing, software
%% distributed under the License is distributed on an "AS IS" BASIS,
%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
%% See the License for the specific language governing permissions and
%% limitations under the License.
%%
%% %CopyrightEnd%
%%
-module(erts_code_purger).
%% Purpose : Implement system process erts_code_purger
%% to handle code module purging.
-export([start/0, purge/1, soft_purge/1, pending_purge_lambda/3,
finish_after_on_load/2]).
-spec start() -> no_return().
start() ->
register(erts_code_purger, self()),
process_flag(trap_exit, true),
wait_for_request().
wait_for_request() ->
handle_request(receive Msg -> Msg end, []).
handle_request({purge, Mod, From, Ref}, Reqs) when is_atom(Mod), is_pid(From) ->
{Res, NewReqs} = do_purge(Mod, Reqs),
From ! {reply, purge, Res, Ref},
check_requests(NewReqs);
handle_request({soft_purge, Mod, From, Ref}, Reqs) when is_atom(Mod), is_pid(From) ->
{Res, NewReqs} = do_soft_purge(Mod, Reqs),
From ! {reply, soft_purge, Res, Ref},
check_requests(NewReqs);
handle_request({finish_after_on_load, {Mod,Keep}, From, Ref}, Reqs)
when is_atom(Mod), is_boolean(Keep), is_pid(From) ->
NewReqs = do_finish_after_on_load(Mod, Keep, Reqs),
From ! {reply, finish_after_on_load, ok, Ref},
check_requests(NewReqs);
handle_request({test_purge, Mod, From, Type, Ref}, Reqs) when is_atom(Mod), is_pid(From) ->
NewReqs = do_test_purge(Mod, From, Type, Ref, Reqs),
check_requests(NewReqs);
handle_request(_Garbage, Reqs) ->
check_requests(Reqs).
check_requests([]) ->
wait_for_request();
check_requests([R|Rs]) ->
handle_request(R, Rs).
%%
%% Processes that tries to call a fun that belongs to
%% a module that currently is being purged will end
%% up here (pending_purge_lambda) in a suspended state.
%% When the purge operation completes or aborts (soft
%% purge that failed) these processes will be resumed.
%%
pending_purge_lambda(_Module, Fun, Args) ->
%%
%% When the process is resumed, the following
%% scenarios exist:
%% * The code that the fun refers to is still
%% there due to a failed soft purge. The
%% call to the fun will succeed via apply/2.
%% * The code was purged, and a current version
%% of the module is loaded which does not
%% contain this fun. The call will result
%% in an exception being raised.
%% * The code was purged, and no current
%% version of the module is loaded. An attempt
%% to load the module (via the error_handler)
%% will be made. This may or may not succeed.
%% If the module is loaded, it may or may
%% not contain the fun. The call will
%% succeed if the error_handler was able
%% to load the module and loaded module
%% contains this fun; otherwise, an exception
%% will be raised.
%%
apply(Fun, Args).
%% purge(Module)
%% Kill all processes running code from *old* Module, and then purge the
%% module. Return {WasOld, DidKill}:
%% {false, false} there was no old module to purge
%% {true, false} module purged, no process killed
%% {true, true} module purged, at least one process killed
purge(Mod) when is_atom(Mod) ->
Ref = make_ref(),
erts_code_purger ! {purge, Mod, self(), Ref},
receive
{reply, purge, Result, Ref} ->
Result
end.
do_purge(Mod, Reqs) ->
case erts_internal:purge_module(Mod, prepare) of
false ->
{{false, false}, Reqs};
true ->
{DidKill, NewReqs} = check_proc_code(erlang:processes(),
Mod, true, Reqs),
true = erts_internal:purge_module(Mod, complete),
{{true, DidKill}, NewReqs}
end.
%% soft_purge(Module)
%% Purge old code only if no procs remain that run old code.
%% Return true in that case, false if procs remain (in this
%% case old code is not purged)
soft_purge(Mod) ->
Ref = make_ref(),
erts_code_purger ! {soft_purge, Mod, self(), Ref},
receive
{reply, soft_purge, Result, Ref} ->
Result
end.
do_soft_purge(Mod, Reqs) ->
case erts_internal:purge_module(Mod, prepare) of
false ->
{true, Reqs};
true ->
{PurgeOp, NewReqs} = check_proc_code(erlang:processes(),
Mod, false, Reqs),
{erts_internal:purge_module(Mod, PurgeOp), NewReqs}
end.
%% finish_after_on_load(Module, Keep)
%% Finish after running on_load function. If Keep is false,
%% purge the code for the on_load function.
finish_after_on_load(Mod, Keep) ->
Ref = make_ref(),
erts_code_purger ! {finish_after_on_load, {Mod,Keep}, self(), Ref},
receive
{reply, finish_after_on_load, Result, Ref} ->
Result
end.
do_finish_after_on_load(Mod, Keep, Reqs) ->
erlang:finish_after_on_load(Mod, Keep),
case Keep of
true ->
Reqs;
false ->
case erts_internal:purge_module(Mod, prepare_on_load) of
false ->
Reqs;
true ->
{_DidKill, NewReqs} =
check_proc_code(erlang:processes(),
Mod, true, Reqs),
true = erts_internal:purge_module(Mod, complete),
NewReqs
end
end.
%%
%% check_proc_code(Pids, Mod, Hard, Preqs) - Send asynchronous
%% requests to all processes to perform a check_process_code
%% operation. Each process will check their own state and
%% reply with the result. If 'Hard' equals
%% - true, processes that refer 'Mod' will be killed. If
%% any processes were killed true is returned; otherwise,
%% false.
%% - false, and any processes refer 'Mod', 'abort' will
%% be returned; otherwise, 'complete'.
%%
%% We only allow ?MAX_CPC_NO_OUTSTANDING_KILLS
%% outstanding kills. This both in order to avoid flooding
%% our message queue with 'DOWN' messages and limiting the
%% amount of memory used to keep references to all
%% outstanding kills.
%%
-define(MAX_CPC_NO_OUTSTANDING_KILLS, 10).
-record(cpc_static, {hard, module, tag, purge_requests}).
-record(cpc_kill, {outstanding = [],
no_outstanding = 0,
waiting = [],
killed = false}).
check_proc_code(Pids, Mod, Hard, PReqs) ->
Tag = erlang:make_ref(),
CpcS = #cpc_static{hard = Hard,
module = Mod,
tag = Tag,
purge_requests = PReqs},
cpc_receive(CpcS, cpc_init(CpcS, Pids, 0), #cpc_kill{}, []).
cpc_receive(#cpc_static{hard = true} = CpcS,
0,
#cpc_kill{outstanding = [], waiting = [], killed = Killed},
PReqs) ->
%% No outstanding cpc requests. We did a hard check, so result is
%% whether or not we killed any processes...
cpc_result(CpcS, PReqs, Killed);
cpc_receive(#cpc_static{hard = false} = CpcS, 0, _KillState, PReqs) ->
%% No outstanding cpc requests and we did a soft check that succeeded...
cpc_result(CpcS, PReqs, complete);
cpc_receive(#cpc_static{tag = Tag} = CpcS, NoReq, KillState0, PReqs) ->
receive
{check_process_code, {Tag, _Pid}, false} ->
%% Process not referring the module; done with this process...
cpc_receive(CpcS, NoReq-1, KillState0, PReqs);
{check_process_code, {Tag, Pid}, true} ->
%% Process referring the module...
case CpcS#cpc_static.hard of
false ->
%% ... and soft check. The whole operation failed so
%% no point continuing; fail straight away. Garbage
%% messages from this session will be ignored
%% by following sessions...
cpc_result(CpcS, PReqs, abort);
true ->
%% ... and hard check; schedule kill of it...
KillState1 = cpc_sched_kill(Pid, KillState0),
cpc_receive(CpcS, NoReq-1, KillState1, PReqs)
end;
{'DOWN', MonRef, process, _, _} ->
KillState1 = cpc_handle_down(MonRef, KillState0),
cpc_receive(CpcS, NoReq, KillState1, PReqs);
PReq when element(1, PReq) == purge;
element(1, PReq) == soft_purge;
element(1, PReq) == test_purge ->
%% A new purge request; save it until later...
cpc_receive(CpcS, NoReq, KillState0, [PReq | PReqs]);
_Garbage ->
%% Garbage message; ignore it...
cpc_receive(CpcS, NoReq, KillState0, PReqs)
end.
cpc_result(#cpc_static{purge_requests = PReqs}, NewPReqs, Res) ->
{Res, PReqs ++ cpc_reverse(NewPReqs)}.
cpc_reverse([_] = L) -> L;
cpc_reverse(Xs) -> cpc_reverse(Xs, []).
cpc_reverse([], Ys) -> Ys;
cpc_reverse([X|Xs], Ys) -> cpc_reverse(Xs, [X|Ys]).
cpc_handle_down(R, #cpc_kill{outstanding = Rs,
no_outstanding = N} = KillState0) ->
try
NewOutst = cpc_list_rm(R, Rs),
KillState1 = KillState0#cpc_kill{outstanding = NewOutst,
no_outstanding = N-1},
cpc_sched_kill_waiting(KillState1)
catch
throw : undefined -> %% Triggered by garbage message...
KillState0
end.
cpc_list_rm(_R, []) ->
throw(undefined);
cpc_list_rm(R, [R|Rs]) ->
Rs;
cpc_list_rm(R0, [R1|Rs]) ->
[R1|cpc_list_rm(R0, Rs)].
cpc_sched_kill_waiting(#cpc_kill{waiting = []} = KillState) ->
KillState;
cpc_sched_kill_waiting(#cpc_kill{outstanding = Rs,
no_outstanding = N,
waiting = [P|Ps]} = KillState) ->
R = erlang:monitor(process, P),
exit(P, kill),
KillState#cpc_kill{outstanding = [R|Rs],
no_outstanding = N+1,
waiting = Ps,
killed = true}.
cpc_sched_kill(Pid, #cpc_kill{no_outstanding = N, waiting = Pids} = KillState)
when N >= ?MAX_CPC_NO_OUTSTANDING_KILLS ->
KillState#cpc_kill{waiting = [Pid|Pids]};
cpc_sched_kill(Pid,
#cpc_kill{outstanding = Rs, no_outstanding = N} = KillState) ->
R = erlang:monitor(process, Pid),
exit(Pid, kill),
KillState#cpc_kill{outstanding = [R|Rs],
no_outstanding = N+1,
killed = true}.
cpc_request(#cpc_static{tag = Tag, module = Mod}, Pid) ->
erts_internal:check_process_code(Pid, Mod, [{async, {Tag, Pid}}]).
cpc_init(_CpcS, [], NoReqs) ->
NoReqs;
cpc_init(CpcS, [Pid|Pids], NoReqs) ->
cpc_request(CpcS, Pid),
cpc_init(CpcS, Pids, NoReqs+1).
% end of check_proc_code() implementation.
%%
%% FOR TESTING ONLY
%%
%% do_test_purge() is for testing only. The purge is done
%% as usual, but the tester can control when to enter the
%% specific phases.
%%
do_test_purge(Mod, From, true, Ref, Reqs) ->
{Res, NewReqs} = do_test_hard_purge(Mod, From, Ref, Reqs),
From ! {test_purge, Res, Ref},
NewReqs;
do_test_purge(Mod, From, false, Ref, Reqs) ->
{Res, NewReqs} = do_test_soft_purge(Mod, From, Ref, Reqs),
From ! {test_purge, Res, Ref},
NewReqs;
do_test_purge(_, _, _, _, Reqs) ->
Reqs.
do_test_soft_purge(Mod, From, Ref, Reqs) ->
PrepRes = erts_internal:purge_module(Mod, prepare),
TestRes = test_progress(started, From, Ref, ok),
case PrepRes of
false ->
_ = test_progress(continued, From, Ref, TestRes),
{true, Reqs};
true ->
{PurgeOp, NewReqs} = check_proc_code(erlang:processes(),
Mod, false, Reqs),
_ = test_progress(continued, From, Ref, TestRes),
{erts_internal:purge_module(Mod, PurgeOp), NewReqs}
end.
do_test_hard_purge(Mod, From, Ref, Reqs) ->
PrepRes = erts_internal:purge_module(Mod, prepare),
TestRes = test_progress(started, From, Ref, ok),
case PrepRes of
false ->
_ = test_progress(continued, From, Ref, TestRes),
{{false, false}, Reqs};
true ->
{DidKill, NewReqs} = check_proc_code(erlang:processes(),
Mod, true, Reqs),
_ = test_progress(continued, From, Ref, TestRes),
true = erts_internal:purge_module(Mod, complete),
{{true, DidKill}, NewReqs}
end.
test_progress(_State, _From, _Ref, died) ->
%% Test process died; continue so we wont
%% leave the system in an inconsistent
%% state...
died;
test_progress(started, From, Ref, ok) ->
From ! {started, Ref},
Mon = erlang:monitor(process, From),
receive
{'DOWN', Mon, process, From, _} -> died;
{continue, Ref} -> erlang:demonitor(Mon, [flush]), ok
end;
test_progress(continued, From, Ref, ok) ->
From ! {continued, Ref},
Mon = erlang:monitor(process, From),
receive
{'DOWN', Mon, process, From, _} -> died;
{complete, Ref} -> erlang:demonitor(Mon, [flush]), ok
end.
